Gypsum plaster-based material containing an edta metal complex

ABSTRACT

A plaster-based material, in particular a plasterboard intended for the interior fitting of dwellings, contains a metal complex of EDTA. The plaster-based material is used for reducing the amount of volatile organic compounds present in the atmosphere inside dwellings, offices or public buildings.

The invention relates to a plaster-based material that is capable of reducing the amount of volatile organic compounds in the ambient air, in particular a plasterboard intended for the interior fitting of dwellings.

Very diverse composite materials are used in the field of construction and of fitment of buildings in general, especially dwellings or offices or public buildings (museums, cinemas, concert halls, etc.). Some of these materials such as sound and/or heat insulators, wood panels, and decorative and furniture elements, use adhesives, paints and varnishes based on resins that contain or release over time volatile organic compounds. These compounds are found in the ambient air and, although the amount thereof appears low they may in the long run trouble or even impair the health of individuals exposed thereto.

In recent years, the proportion of volatile organic compounds in the abovementioned resins has greatly increased due to stricter regulations. However, attempts to replace these resins with others free of volatile organic compounds have been unfruitful since the proposed replacement resins are more expensive and the products obtained have lower performance qualities.

The aim of the present invention is to reduce the content of volatile organic compounds inside buildings, in particular buildings for use as dwellings or offices and public buildings, so as to improve the quality of the ambient air. The targeted volatile organic compounds are more particularly aldehydes, ketones and aromatic compounds.

To achieve this aim, the present invention proposes a plaster-based material, especially a plasterboard, containing a metal complex of ethylenediaminetetraacetic acid (referred to hereinbelow as the “metal complex of EDTA”).

Another subject of the invention concerns the use of the said plaster-based material for reducing the amount of volatile organic compounds in the interior air of buildings, in particular aldehydes, ketones and aromatic compounds.

In the present patent application, the term “volatile organic compound” denotes a compound containing carbon and at least one of the following elements: hydrogen, halogen, oxygen, sulfur, phosphorus, silicon and nitrogen, with the exception of carbon oxides and mineral carbonates and bicarbonates, which have a vapour pressure at least equal to 0.01 kPa at a temperature of 293.15 K. The volatile organic compounds that are most particularly targeted by the present invention are compounds containing carbon, hydrogen and oxygen, especially aromatic compounds and ketones.

In the metal complex of EDTA in accordance with the invention, the metal is preferably chosen from sodium, potassium, calcium, cerium, iron, copper and zinc, and advantageously zinc.

The total amount of metal complex of EDTA to be used generally ranges from 0.0001 to 40 parts by weight per 100 parts by weight of plaster, preferably from 0.001 to 10 parts and advantageously from 0.05 to 5 parts.

The plaster-based material may also contain additives that improve the physicochemical properties of the final product and afford good manufacturing and application conditions. The said material may thus comprise the following additives in the following weight proportions, expressed per 100 parts by weight of plaster:

-   -   0.1 to 15 parts of an adhesion agent whose function is to         increase the adhesion of the paper coating to the plaster, for         example a starch, especially pretreated with an acid, a dextrin         or a vegetable flour, especially wheat or corn flour,     -   0.001 to 10 parts of a setting accelerator, for example hydrated         calcium sulfate or potassium sulfate,     -   0 to 10 parts of a biocide, for example sodium omadine,     -   0.0001 to 1 part of a foaming agent whose role is to create         pores so as to reduce the density of the final product, in         particular of plasterboards. An example that may be mentioned is         sodium lauryl sulfate,     -   0 to 10 parts of at least one water repellent, for example a         siloxane or a polysiloxane,     -   0 to 20 parts of at least one fire retardant, for example         vermiculite, silica, especially of micrometric size, a clay or         metal fibres,     -   0 to 20 parts of at least one reinforcer, for example polymer         fibres, mineral fibres, especially glass fibres, and animal or         vegetable fibres,     -   0 to 20 parts of an agent capable of trapping formaldehyde, for         example acetoacetamide, adipic acid dihydrazide and a protein,         and     -   0 to 20 parts of a material having a high specific surface area,         for example an active charcoal or a zeolite.

The manufacture of plaster panels, in particular a plasterboard, is known per se.

Although the invention is more particularly described with regard to plaster panels, it is not limited to this type of material and includes plaster-based materials in any form whatsoever (powder, rendering, mortar, mastic, tile).

The plasterboard is formed via a continuous process which consists in mixing powdered calcined gypsum (calcium sulfate hemihydrate) with water to form a paste which is continuously deposited between two sheets of paper. The product formed is pressed to obtain the desired thickness, and it is then transported continuously on a conveyor over a distance allowing the paste to achieve a level of hardening sufficient to be able to cut into boards of given length. The boards are then dried in an oven so as to remove the excess water.

Conventionally, the powder components of the paste comprise calcium sulfate hemihydrate (CaSO₄.0.5H₂O; calcined gypsum) and the optional additives described above. The calcined gypsum undergoes a hydration reaction in the presence of water and becomes transformed into calcium sulfate dihydrate (CaSO₄.2H₂O:gypsum).

The amount of calcined gypsum used to form the paste varies according to the nature of the panel to be manufactured, generally from 40 to 150 parts by weight per 100 parts by weight of water, preferably from 60 to 120 parts.

The thickness of the board may vary within a wide range, for example from 6 to 25 mm.

The metal complex of EDTA may be introduced into the plasterboard in various ways.

According to a first preferred embodiment, the metal complex of EDTA is added to the calcined gypsum paste before it is deposited between the sheets of paper.

The addition of metal complex of EDTA may take place during the manufacture of paste, for example by simultaneously or successively introducing the calcined gypsum and the abovementioned compounds into water, or after the paste has been obtained. The simultaneous addition of the constituents is advantageous since it is easier to perform.

This embodiment affords uniform distribution of the metal complex of EDTA in the paste. According to a second embodiment, a layer of low thickness, generally less than 2 mm and preferably less than 1 mm, of a calcined gypsum paste containing the metal complex of EDTA is deposited on the first sheets of paper (lower), followed by the calcined gypsum paste, and finally the second sheets of paper (upper). The application of the paste containing the metal complex of EDTA may take place via any means known to those skilled in the art, for example via the roller coating technique. This manner of proceeding makes it possible to apply the metal complex of EDTA to one face of the plasterboard and to only a part of the thickness.

According to a third embodiment, the metal complex of EDTA is added into or onto the sheet(s) of paper serving as coating. The addition may take place during the manufacture of the paper, for example in the suspension of cellulose fibres, or on at least one face of the sheet of paper, for example by spraying.

The plaster-based material in accordance with the present invention may be in the form of a powder (plaster, rendering, mortar), a paste (mastic, pointing material), a tile or a plaster panel. As more particularly regards the plaster panel, it may be a bare board or a board coated on at least one of its faces with a sheet of paper, an acoustic panel comprising perforations, a panel of plaster and mineral wool or wood, or a board reinforced with fibres or a fabric.

The plaster-based material in accordance with the invention may be used on walls, ceilings and floors, especially for coating or pointing plaster or cement panels or, as regards panels, for forming facings, partitions and suspended ceilings.

The use of the plaster-based material inside a building on a place of dwelling, public place or workplace makes it possible to reduce the amount of volatile organic compounds present in the atmosphere, which is consequently found to be made healthier.

The examples that follow illustrate the invention without, however, limiting it.

EXAMPLE 1

a) Manufacture of the Plaster-Based Material

995 g of calcium sulfate hemihydrate, 5.2 g of starch, 0.1 g of ground gypsum, 1.2 g of zinc-EDTA complex (sold by the company Synthron) and 850 g of water are placed in a mixer.

The mixture is stirred for 60 seconds in order to obtain a paste.

The paste is poured into a grass mould (250 mm×200 mm) lined on its inner face with a sheet of paper, and a second sheet of paper cut to the sizes of the mould is then applied on the paste.

After setting to a solid, the plasterboard is removed from the mould. It is then dried in an oven whose atmosphere is saturated with water, under the following conditions: at 180° C. until 80% of the water is removed, at 100° C. until 95% of the water is removed and at 40° C. for 24 hours.

The board is wrapped in an airtight bag that is resistant to ultraviolet rays.

For comparative purposes, a board not containing any zinc-EDTA complex (comparative example) was prepared under the same conditions.

b) Capacity for Trapping Volatile Organic Compounds

The measurement of the capacity for trapping volatile organic compounds (acetaldehyde, acetone and benzene) is performed in a gastight test chamber.

The plasterboard (100 mm×20 mm; 125 g) is placed in the test chamber, and chamber is then hermetically closed. A continuous stream of air (relative humidity: 50%) containing 20 ppb of the volatile organic compound to be tested is circulated in the chamber at a rate of 250 ml/min.

The measurement of the amount of volatile organic compound is performed in real-time using an FTICR (Fourier transform ion cyclotron resonance) mass spectrometer equipped with a 1 Tesla magnet. The measurement principle is as follows: a semi-porous flat membrane made of polydimethylsiloxane (PDMS) acting as a barrier between the pressure at the chamber outlet (atmospheric pressure) and the vacuum of the mass spectrometer is used. The pressure difference on either side of the membrane and the semi-porous nature of the membrane are such that the volatile organic compounds migrate more rapidly across the membrane than the other molecules contained in the injected air (oxygen, nitrogen, argon, carbon dioxide and water). This results in and enrichment in volatile organic compounds and hence greater sensitivity of detection by the mass spectrometer.

The results given in the table below correspond to a mean value established on a series of three samples of the same plasterboard. The table indicates the percentage reduction in the content of volatile organic compounds below:

Benzene Xylene Cyclohexanone (%) (%) (%) Ex. 1 52 52 70 Comparative Ex. 0 0 0 

1. A plaster-based material, comprising a metal complex of EDTA.
 2. The plaster-based material according to claim 1, wherein a total amount of the metal complex of EDTA ranges from 0.0001 to 40 parts by weight per 100 parts by weight of plaster.
 3. The plaster-based material according to claim 1, wherein the metal in the metal complex of EDTA is chosen from sodium, potassium, calcium, cerium, iron, copper and zinc, preferably zinc.
 4. The plaster-based material according to claim 1, further comprising the following additives in the following weight proportions, expressed per 100 parts by weight of plaster: 0.1 to 15 parts of an adhesion agent, 0.001 to 10 parts of a setting accelerator, 0 to 10 parts of a biocide, 0,0001 to 1 part of a foaming agent, 0 to 10 parts of at least one water repellent, 0 to 20 parts of at least one fire retardant, 0 to 20 parts of at least one reinforcer, 0 to 20 parts of an agent capable of trapping formaldehyde, 0 to 20 parts of a material having a high specific surface area.
 5. The plaster-based material according to claim 1, wherein the plaster-based material is in the form of a powder, a paste or a plaster panel.
 6. The plaster-based material according to claim 5, wherein the plaster-based material is a plasterboard.
 7. A method comprising utilizing a material according to claim 1 for reducing the amount of volatile organic compounds in the interior air of buildings.
 8. The method according to claim 7, wherein the volatile organic compounds are aromatic compounds and ketones.
 9. The plaster-based material according to claim 2, wherein the total amount of the metal complex of EDTA ranges from 0.001 to 10 parts by weight per 100 parts by weight of plaster.
 10. The plaster-based material according to claim 9, wherein the total amount of the metal complex of EDTA ranges from 0.05 to 5 parts by weight per 100 parts by weight of plaster.
 11. The plaster-based material according to claim 3, wherein the metal in the metal complex of EDTA is zinc.
 12. The plaster-based material according to claim 4, wherein the adhesion agent is a starch, a dextrin or a vegetable flour.
 13. The plaster-based material according to claim 4, wherein the setting accelerator is hydrated calcium sulfate or potassium sulfate.
 14. The plaster-based material according to claim 4, wherein the biocide is sodium omadine.
 15. The plaster-based material according to claim 4, wherein the foaming agent is sodium lauryl sulfate.
 16. The plaster-based material according to claim 4, wherein the at least one water repellent is a siloxane or a polysiloxane.
 17. The plaster-based material according to claim 4, wherein the at least one fire retardant is vermiculite, silica, a clay or metal fibres.
 18. The plaster-based material according to claim 4, wherein the at least one reinforcer is polymer fibres, mineral fibres, animal or vegetable fibres.
 19. The plaster-based material according to claim 4, wherein the agent capable of trapping formaldehyde is acetoacetamide, adipic acid dihydrazide or a protein.
 20. The plaster-based material according to claim 4, wherein the material having a high specific surface area is an active charcoal or a zeolite. 